Arc based adaptive control system for an electrosurgical unit

ABSTRACT

A system and method for performing electrosurgical procedures are disclosed. The system includes an electrosurgical generator adapted to supply electrosurgical energy to tissue in form of one or more electrosurgical waveforms having a crest factor and a duty cycle. The system also includes sensor circuitry adapted to measure impedance and to obtain one or more measured impedance signals. The sensor circuitry is further adapted to generate one or more arc detection signals upon detecting an arcing condition§. The system further includes a controller adapted to generate one or more target control signals as a function of the measured impedance signals and to adjust output of the electrosurgical generator based on the arc detection signal. An electrosurgical instrument is also included having one or more active electrodes adapted to apply electrosurgical energy to tissue.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 11/409,574 entitled “ARC BASED ADAPTIVE CONTROLSYSTEM FOR AN ELECTROSURGICAL UNIT” filed by Robert H. Wham on Apr. 24,2006, now U.S. Pat. No. 7,651,492,the entire contents of which arehereby incorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to electrosurgical generators. Moreparticularly, the present disclosure relates to a system and method forcontrolling output of an electrosurgical generator. The electrosurgicalgenerator includes a sensing feedback control system and an arc-basedadaptive control system which adjusts output in response to arcing.

2. Background of Related Art

Energy based tissue treatment is well known in the art. Various types ofenergy (e.g., electrical, ultrasonic, microwave, cryo, heat, laser,etc.) are applied to tissue to achieve a desired result. Electrosurgeryinvolves application of high radio frequency electrical current to asurgical site to cut, ablate, coagulate send or otherwise seal tissue.In monopolar electrosurgery, a source or active electrode delivers radiofrequency energy from the electrosurgical generator to the tissue and areturn electrode carries the current back to the generator. In monopolarelectrosurgery, the source electrode is typically part of the surgicalinstrument held by the surgeon and applied to the tissue to be treated.A patient return electrode is placed remotely from the active electrodeto carry the current back to the generator.

In bipolar electrosurgery, one of the electrodes of the hand-heldinstrument functions as the active electrode and the other as the returnelectrode. The return electrode is placed in close proximity to theactive electrode such that an electrical circuit is formed between thetwo electrodes (e.g., electrosurgical forceps). In this manner, theapplied electrical current is limited to the body tissue positionedbetween the electrodes. When the electrodes are sufficiently separatedfrom one another, the electrical circuit is open and thus inadvertentcontact with body tissue with either of the separated electrodes doesnot cause current to flow.

It is known in the art that sensed tissue feedback may be used tocontrol delivery of electrosurgical energy. During application ofelectrosurgical energy, arcing may occur during the course of treatment.Energy arcing is particularly problematic for sensed feedback controlsystems since the systems attempt to adjust to the rapidly occurringchanges in tissue properties caused by arcing.

SUMMARY

According to one aspect of the present disclosure an electrosurgicalsystem is disclosed. The system includes an electrosurgical generatoradapted to supply electrosurgical energy to tissue in form of one ormore electrosurgical waveforms having a crest factor and a duty cycle.The system also includes sensor circuitry adapted to measure impedanceand to obtain one or more measured impedance signals. The sensorcircuitry is further adapted to generate one or more arc detectionsignals upon detecting an arcing condition. The system further includesa controller adapted to generate one or more target control signals as afunction of the measured impedance signals and to adjust output of theelectrosurgical generator based on the arc detection signal. Anelectrosurgical instrument is also included having one or more activeelectrodes adapted to apply electrosurgical energy to tissue.

Another aspect of the present disclosure includes a method forperforming an electrosurgical procedure. The method includes the stepsof: supplying electrosurgical energy from an electrosurgical generatorto tissue in form of one or more electrosurgical waveforms having acrest factor and a duty cycle and measuring impedance to obtain one ormore measured impedance signals and generating one or more detectionsignal upon detecting arcing conditions. The method further includes thesteps of generating one or more target control signals as a function ofthe measured impedance signals and adjusting output of theelectrosurgical generator based on the arc detection signals.

According to a further aspect of the present disclosure anelectrosurgical generator is disclosed. The generator includes an RFoutput stage adapted to supply electrosurgical energy to tissue in formof one or more electrosurgical waveforms having a crest factor and aduty cycle. The generator also includes sensor circuitry adapted tomeasure impedance and to obtain one or more measured impedance signals.The sensor circuitry is further adapted to generate one or more arcdetection signals upon detecting one or more arcing conditions. Thegenerator further includes a controller adapted to generate one or moretarget control signals as a function of the measured impedance signalsand to adjust output of the electrosurgical generator based on the arcdetection signal

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 is a schematic block diagram of an electrosurgical systemaccording to the present disclosure;

FIG. 2 is a schematic block diagram of a generator according to thepresent disclosure; and

FIG. 3 is a flow diagram illustrating a method according to the presentdisclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the present disclosure inunnecessary detail. Those skilled in the art will understand that themethod according to the present disclosure may be adapted to monitor usewith either monopolar or bipolar electrosurgical systems.

FIG. 1 is a schematic illustration of an electrosurgical systemaccording to the present disclosure. The system includes anelectrosurgical instrument 10 having one or more electrodes for treatingtissue of a patient P. The instrument 10 may be either a monopolar typeincluding one or more active electrodes (e.g., electrosurgical cuttingprobe, ablation electrode(s), etc.) or a bipolar type including one ormore active and return electrodes (e.g., electrosurgical sealingforceps). Electrosurgical RF energy is supplied to the instrument 10 bya generator 20 via a supply line 12, which is operably connected to anactive output terminal, allowing the instrument 10 to coagulate, seal,ablate and/or otherwise treat tissue.

If the instrument 10 is a monopolar type instrument then energy may bereturned to the generator 20 through a return electrode (not explicitlyshown) which may be disposed on the patient's body. The system may alsoinclude a plurality of return electrodes which are arranged to minimizethe chances of damaged tissue by maximizing the overall contact areawith the patient P. In addition, the generator 20 and the monopolarreturn electrode may be configured for monitoring so called“tissue-to-patient” contact to insure that sufficient contact existstherebetween to further minimize chances of tissue damage.

If the instrument 10 is a bipolar type instrument, the return electrodeis disposed in proximity to the active electrode (e.g., on opposing jawsof a bipolar forceps). It is also envisioned that the generator 20 mayinclude a plurality of supply and return terminals and a correspondingnumber of electrode leads.

The generator 20 includes input controls (e.g., buttons, activators,switches, touch screen, etc.) for controlling the generator 20. Inaddition, the generator 20 may include one or more display screens forproviding the surgeon with a variety of output information (e.g.,intensity settings, treatment complete indicators, etc.). The controlsallow the surgeon to adjust power of the RF energy, waveform, and otherparameters to achieve the desired waveform suitable for a particulartask (e.g., coagulating, tissue sealing, intensity setting, etc.). It isalso envisioned that the instrument 10 may include a plurality of inputcontrols which may be redundant with certain input controls of thegenerator 20. Placing the input controls at the instrument 10 allows foreasier and faster modification of RF energy parameters during thesurgical procedure without requiring interaction with the generator 20.

FIG. 2 shows a schematic block diagram of the generator 20 having acontroller 24, a high voltage DC power supply 27 (“HVPS”) and an RFoutput phase 28. The HVPS 27 provides high voltage DC power to an RFoutput phase 28 which then converts high voltage DC power into RF energyand delivers the high frequency RF energy to the active electrode 24. Inparticular, the RF output phase 28 generates sinusoidal waveforms ofhigh frequency RF energy. The RE output phase 28 is configured togenerate a plurality of waveforms having various duty cycles, peakvoltages, crest factors, and other parameters. Certain types ofwaveforms are suitable for specific electrosurgical modes. For instance,the RF output phase 28 generates a 100% duty cycle sinusoidal waveformin cut mode, which is best suited for dissecting tissue and a 25% dutycycle waveform in coagulation mode, which is best used for cauterizingtissue to stop bleeding.

The controller 24 includes a microprocessor 25 operably connected to amemory 26 which may be volatile type memory (e.g., RAM) and/ornon-volatile type memory (e.g., flash media, disk media, etc.). Themicroprocessor 25 includes an output port which is operably connected tothe HVPS 27 and/or RF output phase 28 allowing the microprocessor 25 tocontrol the output of the generator 20 according to either open and/orclosed control loop schemes.

A closed loop control scheme or feedback control loop is provided thatincludes sensor circuitry 22 having one or more sensors for measuring avariety of tissue and energy properties (e.g., tissue impedance, tissuetemperature, output current and/or voltage, etc.). The sensor circuitry22 provides feedback to the controller 24. Such sensors are within thepurview of those skilled in the art. The controller 24 then signals theHVPS 27 and/or RF output phase 28 which then adjust DC and/or RF powersupply, respectively. The controller 24 also receives input signals fromthe input controls of the generator 20 or the instrument 10. Thecontroller 24 utilizes the input signals to adjust power outputted bythe generator 20 and/or performs other control functions thereon.

In particular, sensor circuitry 22 is adapted to measure tissueimpedance. This is accomplished by measuring voltage and current signalsand calculating corresponding impedance values as a function thereof atthe sensor circuitry 22 and/or at the microprocessor 25. Power and otherenergy properties may also be calculated based on collected voltage andcurrent signals. The sensed impedance measurements are used as feedbackby the generator 20 for regulating the energy delivery to the tissue.Various types of impedance feedback control schemes are envisioned, suchas for example, impedance matching (wherein power output is adjusted tomatch measured impedance to target impedance), impedance maintenance(epower is adjusted to maintain impedance), etc.

The sensor circuitry 22 obtains impedance signals and sends acorresponding target control signal that is used by the controller 24 toadjust the output of the generator 20. Since the output of the generator20 is adjusted as a function of the measured impedance, the output ofthe generator 20 responds to every fluctuation in the measuredimpedance. While high resolution response times are desirable, certainvariations in impedance may not warrant adjustments to the output of thegenerator 20.

During electrosurgical procedures, it is known that arcing causes rapidchanges in impedance. Impedance fluctuates between arc impedance to opencircuit impedance (e.g., nil). An impedance feedback control scheme thatadjusts the output of the generator 20 in response to impedance changesfor each arc is undesirable. If the output of the generator 20 tracksthe impedance changes caused by arcing too closely, unwanted oscillationin the output may occur. The present disclosure provides an arc-basedadaptive control method for mitigating oscillation and adjusting thebehavior of an impedance feedback control scheme of the controller 24.

FIG. 3 shows an arc-based adaptive control method according to oneembodiment of the present disclosure which is configured to control theoutput of the generator in response to monitored tissue impedance. Instep 100, the instrument 10 engages the tissue and the generator 20supplies electrosurgical energy to the tissue through the instrument 10.In step 110, during application of energy to the tissue, impedance iscontinually monitored by the sensor circuitry 22 and a measuredimpedance signal is obtained. As discussed above, the measured impedancesignal is derived from voltage and current signals.

In step 120, a target control signal is generated by the controller 24as a function of the measured impedance signal. In particular, thetarget control signal is generated by using output control algorithmswhich may operate in a wide variety of ways. For example, the algorithmsmay attempt to match measured impedance signal to predetermined targetimpedance or may simply use look-up tables containing correspondingtarget control signals. The output control algorithms are stored withinthe memory 26 and are executed by the microprocessor 26. Consequently,the target control signal is used to make appropriate adjustments to theoutput of the generator 20.

In step 130, arcing is detectable by monitoring for rapid repeatingchanges in measured impedance signal, target control signal, or voltageand current signal. Since target control signal and voltage and currentsignals are directly related to measured impedance signal, rapid changesin those signals are also indicative of arcing conditions. In otherwords, impedance correlates with arcing—low impedance is measured duringan are condition followed by high impedance when arcing stops. In step140, an arc detection signal is generated. With reference to FIG. 2,this is accomplished by passing the measured impedance tissue signalthrough a high pass filter 29 and then pass the absolute value of thehigh pass through a low pass filter 30. The resulting filtered signal isthe arc detection signal that is scaled and capped (for example by a 0to 1 scale representing the level of arcing, where 1 represents heavyarcing and 0 represents no arcing). The arc detection signal rises asarcing increases and reduces and arcing decreases.

Arcing may also be detected by detecting rapid changes in the targetcontrol signal and/or by detecting rapid changes in either the voltageor current signals. If arcing is detected, the method proceeds to step150 wherein the arc detection signal is used to make adjustments to theoutput control algorithm of the controller 24. This may be achieved bysubstituting the measured impedance signal with an average impedancevalue. By using the average impedance value to obtain the target controlsignal the generator 20 avoids using extreme impedance values associatedwith arcing. Alternatively, the output control algorithm may beconfigured to include selecting the target control signal associatedwith either the minimum or maximum impedance measured during arcing.This selects an impedance signal that is closest to the previouslymeasured impedance ensuring that the impedance signal and, hence, thetarget control signal, do not deviate substantially from other values.Upon detecting arcing, the controller 24 may also stop and/or hold fromissuing any target control signals thereby maintaining the output basedon an immediately preceding measured impedance signal.

In response to arcing, RF generation may be stopped to quickly removethe arcing condition. This may be achieved to shutting down the RFoutput stage 28 and/or the HVPS 27. In addition, the circuit between thepatient and generator 20 may be opened to prevent the RF energy fromreaching tissue.

Other optimizations to the controller 24 are envisioned so that arcingis extinguished or energy delivery is enhanced during arcing. Inparticular, the calculations performed by the output control algorithmmay be modified so that the desired output voltage, current and/or powerare adjusted when arcing is present.

Further, modification to the waveform produced by the RF output stage 28may be made in response to arcing. This may include momentarymodification of the crest factor (i.e., ratio of the peak value to RMSvalue), the waveform and/or the duty cycle of the waveform. Adjustmentsto the crest factor and the duty cycle enhance or extinguish the arc.Low duty cycles tend to provide coagulation behavior whereas high dutycycles tend to provide for better cutting behavior. Thus, momentarilyincreasing the duty cycle of the waveform extinguishes the arc. Otherways of providing arc-based adaptive control include adjusting PID gainof the controller 24 such that the gain is reduced as the level ofarcing increases.

In step 160, after the arcing conditions are removed, the modificationsmade to the controller 24 and/or the waveform are recalibrated andnormal operating conditions are restored.

The arc-based adaptive control method according to the presentdisclosure allows for fast response to changes in non-arcing conditionsand slows down the controller 24 during arcing so that the controllermay readily select an alternate output value for heating a particulartissue type. This limits aggressive arcing behavior (e.g., so calledentry/exit sparking). Another recognizable advantage is thatelectrosurgical systems utilizing arc-based control methods are capableof automatically switching from cutting to coagulation mode. Thus,during low arcing conditions, the system is optimized for cutting, butas the arcing increases the system adjusts so that coagulation isenhanced.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. A method for controlling an electrosurgicalgenerator, the method comprising the steps of: measuring impedance toobtain at least one measured impedance signal; filtering the at leastone measured impedance signal through a high pass filter to obtain anabsolute value thereof; and filtering the absolute value of the at leastone measured impedance signal through a low pass filter to obtain atleast one arc detection signal; and adjusting output of theelectrosurgical generator based on the at least one arc detectionsignal.
 2. A method according to claim 1, further comprising the stepof: scaling the at least one arc detection signal according to a scalerepresenting level of arcing.
 3. A method according to claim 1, whereinthe step of adjusting output of the electrosurgical generator furthercomprises: supplying electrosurgical energy from an electrosurgicalgenerator to tissue in form of at least one electrosurgical waveformhaving a crest factor and a duty cycle; generating at least one targetcontrol signal as a function of the at least one measured impedancesignal; and adjusting the output of the electrosurgical generator bygenerating at least one target control signal as a function of anaverage impedance value.
 4. A method according to claim 3, wherein thestep of adjusting output of the electrosurgical generator furthercomprises: adjusting at least one of the crest factor and the duty cycleof the at least one waveform.
 5. An electrosurgical generator: sensorcircuitry configured to measure impedance and to obtain at least onemeasured impedance signal; a high pass filter configured to filter theat least one measured impedance signal to obtain an absolute valuethereof; a low pass filter configured to filter the absolute value ofthe at least one measured impedance signal to obtain the at least onearc detection signal; and a controller configured to adjust output ofthe electrosurgical generator based on the at least one arc detectionsignal.
 6. An electrosurgical generator according to claim 5, whereinthe controller is further configured to generate at least one targetcontrol signal as a function of the at least one measured impedancesignal.
 7. An electrosurgical generator according to claim 5, whereinthe controller is further configured to generate at least one targetcontrol signal as a function of an average impedance value.
 8. Anelectrosurgical generator according to claim 5, further comprising an RFoutput stage configured to supply electrosurgical energy to tissue inform of at least one electrosurgical waveform having a crest factor anda duty cycle.
 9. An electrosurgical generator according to claim 8,wherein the controller is configured to adjust a crest factor and a dutycycle of the at least one waveform to control the output of the RFoutput.
 10. An electrosurgical generator according to claim 5, whereinthe at least one arc detection signal is scaled to represent the levelof arcing.
 11. An electrosurgical system comprising: an electrosurgicalgenerator configured to supply electrosurgical energy to tissue; sensorcircuitry configured to measure impedance and to obtain at least onemeasured impedance signal; a high pass filter configured to filter theat least one measured impedance signal to obtain an absolute valuethereof; a low pass filter configured to filter the absolute value ofthe at least one measured impedance signal to obtain at least one arcdetection signal; a controller configured to adjust output of theelectrosurgical generator based on the at least one arc detectionsignal; and an electrosurgical instrument including at least one activeelectrode configured to apply electrosurgical energy to tissue.
 12. Anelectrosurgical system according to claim 11, wherein the at least onearc detection signal is scaled to represent the level of arcing.
 13. Anelectrosurgical system according to claim 11, wherein the controller isfurther configured to generate at least one target control signal as afunction of the at least one measured impedance signal.
 14. Anelectrosurgical system according to claim 11, wherein the controller isfurther configured to generate at least one target control signal as afunction of an average impedance value.
 15. An electrosurgical systemaccording to claim 11, wherein the electrosurgical generator isconfigured to supply electrosurgical energy to tissue in form of atleast one electrosurgical waveform having a crest factor and a dutycycle.
 16. An electrosurgical system according to claim 15, wherein thecontroller is configured to adjust a crest factor and a duty cycle ofthe at least one waveform to control the output of the RF output.